Moderate Data Research Articles

Fast symbol-level synchronization for TR-UWB signals using double hybrid DS-TH spreading

A Transmitted Reference (TR) Ultra WideBand (UWB) signal with double hybrid Direct Sequence and Time Hopping (DS-TH) spreading is proposed and its symbol-level synchronization scheme is designed and analyzed. The proposed signaling format can significantly reduce the search space while reducing the spectral lines and eliminating inter-frame interference and multi-user interference. Detailed analysis of the proposed scheme is carried out. Synchronization performance of the proposed signaling format in multipath channel is derived and supported by computer simulation. The search step which is closely associated with the delay of data modulated pulses is analyzed. Using the TH code, the proposed signaling format and synchronization scheme especially works well in moderate and low data rate systems.

Low-bit-rate color image encoder using an adaptive morphological pyramid decomposition

Interest in multiresolution techniques for image processing and coding is increasing steadily. An attractive instance is pyramid decomposition schemes due to their low computational complexity, simple parallel implementation, and ability to produce acceptable color images at moderate data rates. We present an approach combining a modified pyramidal algorithm and mathematical morphology for color image coding applications denoted as the adaptive morphological pyramid coding (AMPC) algorithm. The proposed AMPC pyramidal strategy involves (1) building a multilevel pyramid based on a developed adaptive morphological filter that preserves the significant details (without shape bias) and does not require very high computational cost, and then (2) the resulting pyramid levels (images) are applied to suitable coding techniques including an adaptive 3-D vector quantization (AVQ). The proposed technique gives an average peak SNR (PSNR) in the range 46.78 to 50.7 dB when no additional coding is applied. When AVQ and differential pulse code modulation (DPCM) are applied to the pyramid levels an average PSNR varies in the range 22.2 to 37.8 dB) at bit rates in the range 0.07 to 1.51 bpp is obtained. When compared with JPEG/JPEG2000, embedded zero-tree wavelet (EZW) coding and set partition in hierarchical trees (SPIHT), the proposed algorithm provides comparable reconstruction quality.

Yb-doped fiber amplifier for deep-space optical communications

A custom-developed high-power laser based on a Yb-doped amplifier is characterized as a transmitter for deep-space optical communications. The key requirements are high peak power at moderate data rates with good beam quality. The transient pulse dynamics are modeled via a simple rate equation approach and reveal a qualitative agreement with the pulsed performance. Peak powers were obtained up to 8 kW for a 22-ns pulsewidth at a 3.5-kHz repetition rates. The peak power dropped significantly as the repetition rate was increased to 50 kHz.

Pulse-coded multiple access in space optical communications

There is interest in space-based wireless optical networks with nonsynchronous multiple access capability. Since space links are usually power-limited, pulsing is necessary to accomplish the multiple accessing and data transmission. In this paper, a nonsynchronous pulsed multiple-access optical-space system using code sequences for identifying stations is considered. Both OOK and PPM data encoding is considered and the link data rates and bit error probabilities (PE) are examined. It is shown that the achievable data rates are limited by the multiple access coding and the link SNR, while the PE can be either crosstalk or power-limited. It appears that moderate data rates (tens of Mb/s) are feasible with networks of about 5-20 stations even with low-link SNR. >

Color image coding using morphological pyramid decomposition

Presents a new algorithm that utilizes mathematical morphology for pyramidal coding of color images. The authors obtain lossy color image compression by using block truncation coding at the pyramid levels to attain reduced data rates. The pyramid approach is attractive due to low computational complexity, simple parallel implementation, and the ability to produce acceptable color images at moderate data rates. In many applications, the progressive transmission capability of the algorithm is very useful. The authors show experimental results for color images at data rates of 1.89 bits/pixel.

InGaAsP channel HFET's on InP for OEIC applications

A model for the calculation of the input noise of a high impedance photoreceiver is proposed, taking into account the contributions of low-frequency characteristics of the FET. Simulations based on this approach show that excess gate leakage current and low-frequency excess noise, usually observed in InGaAs channel FET's, strongly penalize the photoreceiver sensitivity for low to medium data rates. New InGaAsP channel HFET's have been developed and fabricated to solve those problems, dc measurements on 1/spl times/100 /spl mu/m/sup 2/ gate HFET's show good I/sub ds/-V/sub ds/ characteristics with associated gate leakage currents lower than 200 nA. Promising ft of 18 GHz and f/sub max/ of 40 GHz have been recorded on 0.5/spl times/200 /spl mu/m/sup 2/ gate transistors. Low-frequency gate and channel noise measurements demonstrate the suitability of InGaAsP channel HFET structure and technology for low noise applications. A hybrid pin-HFET high impedance photoreceiver has been assembled with a 1/spl times/150 /spl mu/m/sup 2/ gate transistor. A very close agreement is found between photoreceiver input noise predicted by our model and experimental results. Record sensitivities of 34.8 dBm at 622 Mbit/s and -28.7 dBm at 2.5 Gbit/s are inferred from noise measurements, confirming the strong potential of InGaAsP channel HFET's for the fabrication of high sensitivity photoreceivers operating at moderate data rates.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Adaptive Receiver for Digital Communication Over HF Channels

The fading characteristics of the HF channel make communication over this channel difficult, even at moderate data rates. In this correspondence, a practical communication system is presented which has a near-optimal receiver for data detection and adaptive optimization of the receiver to channel parameters. The channel tracking is performed during the training sequence as well as during the detected data sequence. The receiver is fast converging, therefore suitable for frequency hopping. The correspondence presents the performance obtained on fading HF channels and the computational complexity via comparisons to previously published results. The performance is shown to be superior at comparable computational complexity.

A microprocessor-based MODEM for underwater remote sensing

The underwater acoustic channel exhibits large dispersion of the signals in time and frequency domains. The dispersion is characterized by broadening and fading of the signals transmitted through it due to multipath propagation and random motion of particles constituting the medium. Conventional modulation/demodulation techniques, even with forward error correction and ARQ techniques and at moderate data rates, are quite ineffective for data communication over this channel. This paper briefly reviews som signalling schemes which might be suitable for the underwater acoustic channel. A comparative evaluation of them is also presented. The paper also describes a microprocessor-based instrumentation of a versatile MODEM which can implement these schemes under program control with a fixed amount of associated hardware.

Fiber-Optical Transmission Between 0.8 and 1.4 μm

The present state of the art and expected development in discrete components for Fiber-optic transmission systems are reviewed. Predicted performance of fiber systems in the 0.85, 1.06, and 1.27 /spl mu/m regions is presented, and the advantages of longer wavelength operation quantified. Itisconcluded that operation near 1.27 /spl mu/m is particularly attractive for a) moderate data rate systems employing LED's and multimode fibers whose chromatic dispersion and attenuation are greatly reduced compared with 0.85 and 1.06 /spl mu/m, and b) high data rate systems employing lasers and monomode fibers. In systems employing lasers and graded index multimode fibers, the advantage of 1.27/spl mu/m versus 1.06 /spl mu/m operation is not as pronounced, although transmission distances at both of these longer wavelengths are significantly increased from those at 0.85 /spl mu/m.

Fiber-optical transmission between 0.8 and 1.4 µm

The present state of the art and expected development in discrete components for fiber-optic transmission systems are reviewed. Predicted performance of fiber systems in the 0.85, 1.06, and 1.27 µm regions is presented, and the advantages of longer wavelength operation quantified. It is concluded that operation near 1.27 µm is particularly attractive for a) moderate data rate systems employing LED's and multimode fibers whose chromatic dispersion and attenuation are greatly reduced compared with 0.85 and 1.06 µm, and b) high data rate systems employing lasers and monomode fibers. In systems employing lasers and graded index multimode fibers, the advantage of 1.27 µm versus 1.06 µm operation is not as pronounced, although transmission distances at both of these longer wavelengths are significantly increased from those at 0.85 µm.

The Residual Encoder--An Improved ADPCM System for Speech Digitization

An improved system for speech digitization using adaptive differential pulse-code modulation (ADPCM) is described. The system uses an adaptive predictor, an adaptive quantizer, and a variable length source coding scheme to achieve a 4-5 dB increase in signal-to-noise ratio over previous ADPCM. The increase can be used to improve speech quality at moderate data rates on the order of 16 kbits/s or to retain the same quality and reduce the data rate to 9.6 kbits/s. The latter alternative permits the use of narrow-band channels. The implementation complexity is on the same order as other ADPCM systems.